Spatiotemporal features of neurovascular (un)coupling with stimulus-induced activity and hypercapnia challenge in cerebral cortex and olfactory bulb.

Carbon dioxide (CO2) is traditionally considered as metabolic waste, yet its regulation is critical for brain function. It is well accepted that hypercapnia initiates vasodilation, but its effect on neuronal activity is less clear. Distinguishing how stimulus- and CO2-induced vasodilatory responses are (dis)associated with neuronal activity has profound clinical and experimental relevance. We used an optical method in mice to simultaneously image fluorescent calcium (Ca2+) transients from neurons and reflectometric hemodynamic signals during brief sensory stimuli (i.e., hindpaw, odor) and CO2 exposure (i.e., 5%). Stimuli-induced neuronal and hemodynamic responses swiftly increased within locally activated regions exhibiting robust neurovascular coupling. However, hypercapnia produced slower global vasodilation which was temporally uncoupled to neuronal deactivation. With trends consistent across cerebral cortex and olfactory bulb as well as data from GCaMP6f/jRGECO1a mice (i.e., green/red Ca2+ fluorescence), these results unequivocally reveal that stimuli and CO2 generate comparable vasodilatory responses but contrasting neuronal responses. In summary, observations of stimuli-induced regional neurovascular coupling and CO2-induced global neurovascular uncoupling call for careful appraisal when using CO2 in gas mixtures to affect vascular tone and/or neuronal excitability, because CO2 is both a potent vasomodulator and a neuromodulator.

Selective Overexpression of Collybistin in Mouse Hippocampal Pyramidal Cells Enhances GABAergic Neurotransmission and Protects against PTZ-Induced Seizures.

Collybistin (CB) is a rho guanine exchange factor found at GABAergic and glycinergic postsynapses that interacts with the inhibitory scaffold protein, gephyrin, and induces accumulation of gephyrin and GABA type-A receptors (GABAARs) to the postsynapse. We have previously reported that the isoform without the src homology 3 (SH3) domain, CBSH3-, is particularly active in enhancing the GABAergic postsynapse in both cultured hippocampal neurons as well as in cortical pyramidal neurons after chronic in vivo expression in in utero electroporated (IUE) rats. Deficiency of CB in knock-out (KO) mice results in absence of gephyrin and gephyrin-dependent GABAARs at postsynaptic sites in several brain regions, including hippocampus. In the present study, we have generated an adeno-associated virus (AAV) that expresses CBSH3- in a cre-dependent manner. Using male and female VGLUT1-IRES-cre or VGAT-IRES-cre mice, we explore the effect of overexpression of CBSH3- in hippocampal pyramidal cells or hippocampal interneurons. The results show that: (1) the accumulation of gephyrin and GABAARs at inhibitory postsynapses in hippocampal pyramidal neurons or interneurons can be enhanced by CBSH3- overexpression; (2) overexpression of CBSH3- in hippocampal pyramidal cells can enhance the strength of inhibitory neurotransmission; and (3) these enhanced inhibitory synapses provide protection against pentylenetetrazole (PTZ)-induced seizures. The results indicate that this AAV vector carrying CBSH3- can be used for in vivo enhancement of GABAergic synaptic transmission in selected target neurons in the brain.

Somatostatin-expressing parafacial neurons are CO2/H+ sensitive and regulate baseline breathing.

Glutamatergic neurons in the retrotrapezoid nucleus (RTN) function as respiratory chemoreceptors by regulating breathing in response to tissue CO2/H+. The RTN and greater parafacial region may also function as a chemosensing network composed of CO2/H+-sensitive excitatory and inhibitory synaptic interactions. In the context of disease, we showed that loss of inhibitory neural activity in a mouse model of Dravet syndrome disinhibited RTN chemoreceptors and destabilized breathing (Kuo et al., 2019). Despite this, contributions of parafacial inhibitory neurons to control of breathing are unknown, and synaptic properties of RTN neurons have not been characterized. Here, we show the parafacial region contains a limited diversity of inhibitory neurons including somatostatin (Sst)-, parvalbumin (Pvalb)-, and cholecystokinin (Cck)-expressing neurons. Of these, Sst-expressing interneurons appear uniquely inhibited by CO2/H+. We also show RTN chemoreceptors receive inhibitory input that is withdrawn in a CO2/H+-dependent manner, and chemogenetic suppression of Sst+ parafacial neurons, but not Pvalb+ or Cck+ neurons, increases baseline breathing. These results suggest Sst-expressing parafacial neurons contribute to RTN chemoreception and respiratory activity.

Influence of Exogenous ß-Hydroxybutyrate on Walking Economy and Rating of Perceived Exertion.

This study investigates the effect of a supplementary ketone, ß-hydroxybutyrate (BHB), on walking economy and ratings of perceived exertion in apparently healthy individuals. In a repeated-measures, crossover design, ten non-aerobically trained participants (three males; seven females) performed two stages of a duration-modified Bruce treadmill protocol. Participants blindly consumed either 1 ounce of an exogenous BHB solution (KETO) or a noncaloric placebo (CON) 30 minutes prior to exercise testing. Blood ketone and glucose concentrations were measured prior to supplementation (baseline), immediately before exercise, and after exercise. Oxygen consumption (VO2), respiratory exchange ratio (RER), energy expenditure (EE), and rating of perceived exertion (RPE) were recorded during the last two minutes of each stage. Blood BHB concentrations were significantly elevated at the pre-exercise and postexercise time points as compared to the CON condition (p < .001), and blood glucose was significantly elevated postexercise in both conditions as compared to baseline levels (p < .001). No significant between-trial differences (p > .05) were found for VO2, RER, EE, or RPE. The intervention of this study did not produce evidence of an ergogenic benefit from BHB supplementation in a healthy subject pool.

The influence of training with heavy rugby balls on selected spin pass variables in youth rugby union players.

The purpose of this study was to investigate the influence of training with heavy rugby balls on selected spin pass variables in youth rugby union players. Pre-training, 14 participants performed rapid spin passes (using right and left hands) at a wall-mounted target, from 7-m and 10-m distances. Horizontal (linear) and spin (longitudinal angular) velocities of the passes were recorded using a 25Hz video camera. Participants also performed right- and left-handed spin passes for maximal distance. The participants were then randomly divided into two equal groups, to train twice weekly for eight weeks, using either normal or heavy rugby balls. Each individual performed 50-90 rapid spin passes ranging from 5m to 12m with each hand per session. Following training, participants were reassessed using the same pre-training protocols. Significant changes were found pre-to-post training for both the normal ball, and heavy ball groups, for 7-m right-handed horizontal (linear) velocities (9.80+/-0.45 to 10.27+/-0.82ms(-1), and 9.42+/-1.04 to 10.19+/-1.03ms(-1), respectively; p=0.029), 10-m left-handed spin (longitudinal angular) velocities (5.13+/-1.60 to 6.08+/-1.30revss(-1), and 4.39+/-1.62 to 5.81+/-0.65revss(-1), respectively; p=0.014), right-handed maximal distance passes (19.0+/-3.6 to 20.6+/-4.0m, and 18.6+/-3.4 to 20.7+/-4.3m, respectively; p=0.001) and left-handed maximal distance passes (15.3+/-3.2 to 18.1+/-2.5m, and 15.0+/-3.0 to 17.6+/-3.7m, respectively; p<0.000). No significant changes could be attributed to training exclusively with the heavy rugby balls. The results of this investigation suggest that intense repetitive passing practice increases a small number of selected spin passing variables in youth rugby union players.